1. Field of the Invention
The present invention pertains to a method and apparatus for processing a video signal, and more particularly to removing (defeating) effects of copy protection signals from a video signal.
2. Description of the Prior Art
U.S. Pat. No. 4,631,603 ('603) by Ryan, issued on Dec. 23, 1986 entitled METHOD AND APPARATUS FOR PROCESSING A VIDEO SIGNAL SO AS TO PROHIBIT THE MAKING OF ACCEPTABLE VIDEO TAPE RECORDINGS THEREOF describes a video signal that is modified so that a television receiver will still provide a normal color picture from the modified video signal while a videotape recording of the modified video signal produces generally unacceptable pictures (incorporated by reference).
The '603 invention relies on the fact that typical videocassette recorder's automatic gain control systems cannot distinguish between the normal sync pulses (including equalizing or broad pulses) of a conventional video signal and added pseudo-sync pulses. Pseudo-sync pulses are defined here as pulses which extend down to a normal sync tip level and which have a duration of a least 0.5 microseconds. A plurality of such pseudo-sync pulses is added to the conventional video during the vertical blanking interval, and each of such pseudo-sync pulses is followed by a positive pulse of suitable amplitude and duration.
As a result, the automatic gain control system in a video-tape recorder will make a fake measurement of video level which causes an improper recording of the video signal. The result is unacceptable picture quality during playback.
U.S. Pat. No. 4,819,098 ('098) by Ryan, issued on Apr. 4, 1989 entitled METHOD AND APPARATUS FOR CLUSTERING MODIFICATIONS MADE TO A VIDEO SIGNAL TO INHIBIT THE MAKING OF ACCEPTABLE VIDEOTAPE RECORDING describes a signal modification so that a television monitor receiver still produces a normal picture from the modified signal, whereas a videotape recording of this signal produces generally unacceptable pictures and is incorporated by reference. Videotape recorders have an automatic gain control circuit which measures the sync level in a video signal and develops a gain correction for keeping the video level applied to an FM modulator in the videotape recording system at a fixed, predetermined value. A plurality of positive pulses are added to a video signal with each immediately following a respective trailing edge of a normally occurring sync pulse. These added pulses are clustered at the vertical blanking interval of each field to minimize the affect of the same on the viewability of the picture defined by the signal while still causing the automatic level control circuit in a recorder to assess the video level at many times its actual value. The sync pulses themselves can also be at a reduced level, in order to enhance the effectiveness of the process.
U.S. Pat. No. 4,695,901 ('901) by Ryan, issued on Oct. 2, 1990 entitled METHOD AND APPARATUS FOR REMOVING PSEUDO-SYNC AND/OR AN AGC PULSES FROM A VIDEO SIGNAL describes removing pseudo-sync pulses and AGC pulses that have been added to a video signal to enable acceptable video recording thereof and is hereby incorporated by reference. The added signals previously interfered with acceptable video recording of the video signal because the automatic gain control of videotape recorders sensed false recording levels, while conventional television receivers were unaffected by those modifications to the video signal. Removal of the added pulses permits acceptable video recording of the previously modified video signal. A selectively-operable clipping circuit is used to remove selected negative-value components (i.e. pseudo-sync pulses)from the video signal, while added AGC pulses are effectively blanked from the video signal with an electrically-operated switch. Both the blanking and clipping functions are selectively achieved by sensing both the normal sync pulses of the video signal and the added pseudo-sync pulses. Method and apparatus are disclosed for "cleaning up" video signals modified by either the pseudo-sync pulses alone, the AGC pulses alone, or combinations thereof.
U.S. Pat. No. 4,336,554 ('554) by Okada et al., issued on Jan. 21, 1992 entitled CODE SIGNAL BLANKING APPARATUS (incorporated by reference) describes a code signal blanking apparatus comprising a switching means operative during a given period of a vertical blanking period of a television signal and a reference level setting means for producing an output of the reference level during said given period when the switching circuit is operative.
U.S. Pat. No. 5,194,965 ('965) by Quan et al., issued on Mar. 16, 1993 entitled METHOD AND APPARATUS FOR DISABLING ANTI-COPY PROTECTION SYSTEM IN VIDEO SIGNALS describes a method and apparatus for disabling the effect of copy-protection signals placed in a recording video signals which is based on differences in the characteristics of television and VCR circuitry and is hereby incorporated by reference. Copy-protect signals include pseudo-sync pulses and/or added AGC pulses in the blanking interval of a video signal. The specific method described includes altering the level of the video signal during the vertical blanking interval, e.g. level-shifting, so as to render the copy-protect signals ineffective to prevent unauthorized copying by a VCR. A circuit for achieving the method includes a sync separator for detecting the vertical blanking interval, pulse generating circuits for producing pulses of predetermined widths during the interval, and a summing circuit for summing the predetermined pulses with copy-protect signals thereby to shift their level. An alternative method includes increasing the effective frequency and / or narrowing of the copy-protect signals during the vertical blanking interval so as to achieve attenuation and/or low-pass filtering in the VCR circuitry to thereby render the signals ineffective in preventing copying. A circuit for achieving this method includes pulse narrowing and/or pulse multiplication circuitry which effectively increases the high-frequency content of the pseudo-sync and/or AGC pulses.
U.S. Pat. No. 5,157,510 ('510) by Quan et al., issued on Oct. 20, 1992 entitled METHOD AND APPARATUS FOR DISABLING ANTI-COPY PROTECTION SYSTEM IN VIDEO SIGNALS USING PULSE NARROWING describes method and apparatus for disabling the effects of copy-protect signals added to a video signal using differences in the characteristics of television and VCR circuitry (incorporated by reference). Copy-protect signals as described include pseudo-sync pulses and/or added AGC pulses in the vertical blanking intervals of a video signal. The specific method described includes increasing the effective frequency of the copy-protect signals during the vertical blanking intervals so as to achieve attenuation and/or low pass filtering in the VCR circuitry to thereby render the signals ineffective in preventing copying. A circuit for achieving this method comprises pulse narrowing and/or pulse multiplication circuitry which effectively increases the high-frequency content of the pseudo-sync and/or AGC pulses.
U.S. patent application 5,625,691 ('691) entitled "VIDEO COPY PROTECTION PROCESS ENHANCEMENT AND VERTICAL PICTURE DISTORTIONS," by Quan issued on Apr. 29, 1997 which is incorporated by reference, discloses defeating the affects of the signal generated by the '603 patent by modifying the relative amplitudes of the pseudo sync pulses to the normal sync pulse so that synchronizing pulse detection system within a recorder will only detect the normal synchronizing pulses, thus permitting normal recording of said copy protection signal.
U.S. patent application 5,633,927 ('927) entitled "VIDEO COPY PROTECTION PROCESS ENHANCEMENT AND VERTICAL PICTURE DISTORTIONS," by Quan issued on May 27, 1997 which is incorporated by reference, discloses various defeat mechanisms the affects of the signal generated by the '603 patent to permit normal recording of said copy protection signal.
U.S. Pat. No. 4,907,093 ('093) entitled "Method and Apparatus for Preventing The Copying of a Video Program," which is incorporated by reference, discloses a method and apparatus for detecting the ordered pairs of pseudo-sync pulses and AGC pulses described in the '603 patent and disabling the recording function of a video cassette recorder. The '093 patent discloses several detection methods.
Additionally, U.S. Pat. No. 4,571,615 ('615) entitled "TIMING GENERATOR FOR SYNC SUPPRESSED TELEVISION SIGNALS," by Robbins et al. issued on Feb. 18, 1986 which is incorporated by reference, discloses a timing signal generator for recovering timing signals in scrambled video signals in which the synchronizing signals are suppressed including a detector responsive to the color burst or chroma in the horizontal blanking interval signal contained on the back porch of a suppressed horizontal blanking interval. The vertical interval is detected as the absence of color burst or chroma in the horizontal blanking interval for a specified time interval, and horizontal sync information is obtained by the detection of the first color burst or chroma in the horizontal blanking interval after an absence of color burst or chroma in the horizontal blanking interval.
All of the defeat methods described in the referenced defeat patents use the vertical and horizontal synchronizing pulses to determine the location of the copy protection signals within a copy protected video signal. There is a need for copy protection defeat mechanisms that do not rely on the horizontal and vertical synchronizing pulses to determine the location of the copy protection signals within a copy protected video signal.